4.3 Weights
47
To do this, Sefficiency uses quality weight for each WPI (W qX ) in order to explicitly quantify pollution influence on the performance of a WUS. Sometimes it is easy
to set those weights:
• Quality weight for treated water supplied to population is one (W qI = 1).
• Quality weights of evapotranspiration (W qET ) and some of non-reusable (W qNR ),
such as evaporation and bottled water are one.
However, in most situations, quality weight of a WPI is less than one and should
be calculated using estimates and measurements having in mind that a water quality
index (or quality weight) “is a weighted average of selected ambient concentrations
of pollutants usually linked to water quality classes” (OECD 2001). What follows is
a small list that can guide in setting quality weights:
• The Water Framework Directive (European Parliament & Council 2000) introduced surface water status and groundwater status, which are general expressions
of the status of a body of surface water or groundwater, respectively. Both include
chemical status and classify waters into clearly defined categories with associated
colours.
• Canadian water quality guidelines for the protection of aquatic life employs Water
Quality Index (CCME 2017), which has a calculator and a user’s manual.
• The main global water quality index for domestic purposes is the Global Drinking
Water Quality Index of the Global Environmental Monitoring System (GEMS)
Water Programme, the United Nations Environment Program (UNEP 2007), and
is based on the Canadian Water Quality Index.
• Chinese Environmental Quality Standards with five classes are “formulated for
implementing the Environmental Protection Law and Law of Water Pollution
Prevention and Control of People’s Republic of China, and to control water
pollution and to protect water resources” (MEEC 1997; MEEC 2018).
• To calculate water footprint, Hoekstra et al. (The water footprint assessment
manual: Setting the global standard 2011) introduced grey water footprint as “an
indicator of freshwater pollution” in order to achieve a water quality objective/
standard. In this context, grey water footprint may be employed to set W qX under
some conditions.
• Food and Agriculture Organisation of the United Nations proposes the use of
leaching fraction (Ayers and Westcot 1994) that is widely employed in irrigation
management to avoid salt accumulation and can be used for setting quality weight
(W qX = 1 − LF X , LF being leaching fraction).
4.3.2 Beneficial Attribute
The beneficial weight (W bX ) is set by focussing on the nature and objectives of
the WUS under consideration without considering its quality (W qX = 1). This is
the usual way that the planning and management of the systems are carried out
today, i.e., water quality of a system is dealt with separately according to its inflow
47
To do this, Sefficiency uses quality weight for each WPI (W qX ) in order to explicitly quantify pollution influence on the performance of a WUS. Sometimes it is easy
to set those weights:
• Quality weight for treated water supplied to population is one (W qI = 1).
• Quality weights of evapotranspiration (W qET ) and some of non-reusable (W qNR ),
such as evaporation and bottled water are one.
However, in most situations, quality weight of a WPI is less than one and should
be calculated using estimates and measurements having in mind that a water quality
index (or quality weight) “is a weighted average of selected ambient concentrations
of pollutants usually linked to water quality classes” (OECD 2001). What follows is
a small list that can guide in setting quality weights:
• The Water Framework Directive (European Parliament & Council 2000) introduced surface water status and groundwater status, which are general expressions
of the status of a body of surface water or groundwater, respectively. Both include
chemical status and classify waters into clearly defined categories with associated
colours.
• Canadian water quality guidelines for the protection of aquatic life employs Water
Quality Index (CCME 2017), which has a calculator and a user’s manual.
• The main global water quality index for domestic purposes is the Global Drinking
Water Quality Index of the Global Environmental Monitoring System (GEMS)
Water Programme, the United Nations Environment Program (UNEP 2007), and
is based on the Canadian Water Quality Index.
• Chinese Environmental Quality Standards with five classes are “formulated for
implementing the Environmental Protection Law and Law of Water Pollution
Prevention and Control of People’s Republic of China, and to control water
pollution and to protect water resources” (MEEC 1997; MEEC 2018).
• To calculate water footprint, Hoekstra et al. (The water footprint assessment
manual: Setting the global standard 2011) introduced grey water footprint as “an
indicator of freshwater pollution” in order to achieve a water quality objective/
standard. In this context, grey water footprint may be employed to set W qX under
some conditions.
• Food and Agriculture Organisation of the United Nations proposes the use of
leaching fraction (Ayers and Westcot 1994) that is widely employed in irrigation
management to avoid salt accumulation and can be used for setting quality weight
(W qX = 1 − LF X , LF being leaching fraction).
4.3.2 Beneficial Attribute
The beneficial weight (W bX ) is set by focussing on the nature and objectives of
the WUS under consideration without considering its quality (W qX = 1). This is
the usual way that the planning and management of the systems are carried out
today, i.e., water quality of a system is dealt with separately according to its inflow